A 36-year-old Scottish aid worker kidnapped two weeks ago in one of the most dangerous parts of Afghanistan might have been killed by the American special operations team sent to rescue her -- and not by her captors, as the U.S. military initially said.

Linda Norgrove, a woman who had spent much of her life helping the poor, was being held in the remote province of Kunar when the British government authorized a rescue mission, according to British officials in London and Western officials in Kabul.

But the mission went horribly wrong when an explosion severely wounded Norgrove and, according to two Western officials, a medic at the scene was unable to revive her.

Over the weekend, U.S. officials gave specific details about how a suicide bomber blew himself up next to Norgrove as the rescue team closed in. But today the U.S. changed its story. Two Western officials say after reviewing footage of the raid filmed from the air -- either by a drone or a satellite -- and interviewing members of the team, it became clear that a grenade thrown by one of the American forces might have caused the explosion that killed her.

"The decision to launch this rescue operation was not an easy one," British Prime Minister David Cameron said in London today, announcing an investigation that will examine exactly what caused Norgrove's death. "I'm clear that the best chance of saving Linda's life was to go ahead, recognizing that any operation was fraught with risk for all those involved and success could by no means be guaranteed."

Today, clearly stung by being proven wrong about the suicide bomber, Western officials in Kabul tried emphasize how difficult the mission was.

Norgrove was being held in a house owned by Mullah Kiftan, a local Taliban commander in a district of Kunar province named after himself, according to local officials. The house was on a "precipice" 8,000 feet high, making landing in the area with a helicopter extremely difficult, according to three Western officials. The special operations forces team flew to the site on a night with no moon and "quick roped" down to the ground, immediately getting into a large and lengthy firefight, during which at least nine militants were killed.

At some point, there was an explosion near Norgrove. U.S. officials say they still have not confirmed the cause of death -- whether from a fragmentation grenade thrown by a member of the rescue team, or from an insurgent bomb somehow triggered by the thrown grenade.

Doubts About Norgrove Rescue Raid

But the shift of blame to American special operations forces sparked new doubts in London and Kabul about whether the raid should have been launched in the first place.

U.S. officials say they launched the raid for two reasons: they were worried Norgrove would be taken to Pakistan, where the U.S. military does not openly operate, and that there was a "very real, direct threat that they would kill her," according to one Western official in Kabul.

And local officials say they also believed insurgents intended to take Norgrove across the border -- and were not going to negotiate until they did so.

The house where she was being held is only about two dozen miles from Pakistan. Intelligence officials had enough information to surround the area, according to three western officials, essentially restricting the militants' movement.

But in the past, American special operations forces have tried to keep militants penned inside Afghanistan, according to one Western official, and failed – New York Times reporter David Rohde was taken across the border into North Waziristan, and Sergeant First Class Bowe Bergdahl is believed to have been taken to the same Pakistani tribal area.

"Those on the ground and in London feared that she was going to be passed up the terrorist chain, which would increase further the already high risk that she would be killed," Cameron said.

Norgrove, the daughter of a charity worker and an engineer, led a $150 million program in eastern Afghanistan, where she worked with a team to build roads and bridges and improve the capabilities of district governments. Her friends and colleagues described her as deeply respectful toward Afghanistan and its culture, eschewing the kinds of security measures that most Westerners take -- especially in the part of the country where she worked.

"Linda had extraordinary composure and inner strength," said Nick Horne, who hiked with Norgrove in northeastern Afghanistan last summer. She had come to love the country so much during her previous time living here, she took three weeks of her annual leave to spend in the Wakhan corridor with three friends.

She left Afghanistan after that trip but returned in January to run the program for Development Alternatives Inc. (DAI), a well-known contractor for the United States International Agency for Development. Westerners working for NGOs and contracting firms such as DAI in Afghanistan have had to severely restrict their movements in the last year and a half as violence in eastern and northern Afghanistan increased rapidly.

Many aid workers say that in the northern and eastern parts of the country, they often can't go to small villages today they used to be able to visit just a year ago.

'The Use of a Hand Grenade Is Ridiculous'

Norgrove was in one of the most dangerous areas in all of Afghanistan -- something that her friends say she was worried about but largely took in stride, confident that keeping a low profile and not traveling with security was the safest way to travel.

"She believed in respecting of other people's environments," said friend Gerard Russell, who also hiked with her last summer. "She believed in getting close to people, and understanding them."

In July a group of Western aid workers were kidnapped and killed in a district north of where Norgrove died. Security has already been severely tightened by Western organizations working in Afghanistan, and many workers will soon not be able to travel much at all.

"It's a blow for people's morale for people who want to work in the field," Russell said. "We should celebrate these people and what they do – while it's still going on."

Elite American special operations forces have become familiar with the rugged landscape of eastern Afghanistan as have they more than doubled targeted raids against mid-level Taliban commanders there this year. They are extremely well trained, but in an operation such as this one, there is a thin line between success and failure.

"These guys are experts, but they're going into a situation they can't control," says a former Army Ranger.

Some former special operations troops criticized the tactics of the team, suggesting they were at fault for the mission's failure.

"The use of a lethal hand grenade in a hostage rescue situation is ridiculous. It's not appropriate," argued Robin Horsfall, a former British special operations soldier, on Al Jazeera English today.

And depending on the speed with which the team had to dispatch to the site, it's possible that they were not the most elite or cohesive group.